Counter-rotating vertical axis wind turbine assembly

ABSTRACT

A vertically-oriented, counter-rotating wind turbine assembly is disclosed. The assembly can include two or more wind turbines, and each adjacent pair of wind turbines is configured to rotate oppositely. The wind turbines are separated by supporting plates, and include a rotor and a stator, respectively. The relative rotation of the rotor and stator generates electricity. The wind turbines are supported above and below by levitation and compression bearings, respectively. A motor can initiate rotation of the wind turbines when the ambient wind is below a break-in speed and above a steady state speed.

CROSS REFERENCE TO RELATED APPLICATION

This non-provisional patent application hereby claims priority toProvisional Patent Application No. 61/421,941, titled Counter-RotatingVertical Axis Wind Turbine Assembly, filed Dec. 10, 2010, which ishereby by incorporated herein in its entirety by reference thereto.

TECHNICAL FIELD

The present disclosure is generally directed to counter-rotating,vertically-oriented, wind turbine assemblies and associated methods.

BACKGROUND

There is an increasing demand for clean, renewable energy sources as webecome more aware of the affect that mass energy consumption has on ourenvironment. There are many sources of energy on Earth, but most of thisenergy is not harnessed. For example, solar energy and wind energy areabundant, but to date have not been adequately harvested and put toproductive use without specialized and usually expensive equipment.Environmentally responsible energy production and harvesting methodsunfortunately still compete in today's marketplace with energy sourcesthat have a more harmful impact on the environment, such as fossilfuels. To be more competitive against fossil fuels, “green” energysources must be as efficient as possible in terms of the energy theyharvest, and in terms of the expense to build, operate, and maintain.

SUMMARY

The present disclosure is directed to a counter-rotating, vertical windturbine assembly. In one embodiment, the counter-rotating, vertical windturbine assembly has two counter-rotating wind turbines axially alignedin a vertical orientation and rotatably disposed on a central shaft. Thewind turbines each include two disks, one on top and one on bottom, withthe vanes extending between the disks. The turbines rotate in oppositedirections so the relative angular velocity of the turbines is equal tothe sum of the magnitude of their respective angular velocities. Inother words, defining the rotation of one turbine as positive and therotation of the other turbine as negative, the relative angular velocityis equal to the difference between their respective angular velocities.The relative rotation is used to generate electricity in at least oneembodiment due to a rotor on one turbine and a stator on the otherturbine forming an alternator. The electricity generated in analternator is generally proportional to the speed at which the rotorrotates relative to the stator. Accordingly, the counter-rotatingturbines of the present disclosure can generate up to at leastapproximately twice the amount of energy produced by a single windturbine rotating relative to a stationary reference. In one embodiment,the assembly includes two axially aligned, counter-rotating,vertical-axis wind turbines coupled to one or more single-rotationalternators to generate electricity from the relative movement betweeneach turbine and a stationary support. The assembly 100 also includes acounter-rotation alternator to generate electricity from the relativemotion between the counter-rotating wind turbines.

To support the wind turbines, the assembly can include a magnetic liftbearing underneath each wind turbine. The magnetic lift bearing supportsthe turbines without contacting the wind turbines, therefore reducingspinning resistance. In some embodiments, the magnetic lift bearings caninclude rare earth magnets, electromagnets, or other suitable magnets.The wind turbines can also have an upper compression magnetic bearingacting downward upon the turbines to help maintain the turbines in asteady rotation path. The compression force of the upper bearings isgenerally less than the levitation force of the lift bearings. In someembodiments, the upper compression bearings can be selectively activatedand deactivated. Accordingly, the upper compression bearings can beswitched on when the turbine has reached a selected rotational speed,and switched off when the turbine is stopped and/or during spininitiation, thereby reducing the initial resistance to start up rotationof the turbine.

In some embodiments, the assembly includes a solar-powered system tohelp spin one or more of the turbines. To overcome an inertial barrierto starting rotation of the turbine, the ambient wind must be above acertain level, called a break-in speed. However, the wind speed requiredfor steady-state operation of the wind turbines is generally lower thanthe break-in speed. In some embodiments, the assembly includes a motorthat starts the turbines spinning. This motor is powered by solar panelson the upper plate or in another exposed location of the assembly. Themotor can also be powered by electricity stored in a battery or othersuitable electrical storage device. The battery can be local with theassembly or (e.g., a rechargeable battery) or in some other location. Insome embodiments, the present disclosure is directed to a method ofinitiating rotation of a wind turbine, comprising detecting an ambientwind speed around the wind turbine, and comparing the wind speed to apredetermined steady-state wind speed and to a break-in wind speed. Ifthe wind turbines are not rotating, and if the wind speed is at or abovethe steady-state wind speed but below the break-in wind speed, themethod can include rotating the wind turbines with a motor until thewind turbines reach a steady-state operating speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a wind turbine assembly in accordancewith embodiments of the present disclosure.

FIG. 2 is an exploded, isometric view of a wind turbine assembly inaccordance with embodiments of the present disclosure.

FIG. 3 is a side cross-sectional view of a wind turbine assemblycomprising a nested alternator in accordance with embodiments of thepresent disclosure.

FIG. 4 is an exploded, isometric view of a wind turbine assembly inaccordance with embodiments of the present disclosure.

FIG. 5 is a partially schematic side cross-sectional view of a windturbine assembly in accordance with embodiments of the presentdisclosure.

FIG. 6 is a flow chart diagram of a method in accordance withembodiments of the present disclosure.

DETAILED DESCRIPTION

Various embodiments of wind turbine assemblies and methods ofmanufacturing and operation in accordance with an aspect of thedisclosure are described below. A person skilled in the relevant artwill also understand that the technology may have additional embodimentsand that the technology may be practiced without several of the detailsof the embodiments described below with reference to FIGS. 1-6.

FIG. 1 of the illustrated embodiment is an isometric view of acounter-rotating, vertical-axis wind turbine (VAWT) assembly 100 inaccordance with embodiments of the present disclosure. FIG. 2 is apartially schematic, exploded, isometric view of the VAWT assembly 100of FIG. 1. The VAWT assembly 100 includes a lower plate 110, a lowerwind turbine 120, a middle plate 130, an upper wind turbine 140, and anupper plate 150. A shaft 160 passes through the wind turbines 120, 140,and the plates 110, 130, and 150. The wind turbines 120, 140 includewind vanes 121 that cause the turbines 120, 140 to rotate around theshaft under pressure from passing wind. The vanes 121 in the respectiveturbines 120, 140 are oriented oppositely, so that wind causes the lowerturbine 120 to rotate in one direction and the upper turbine 140 torotate in an opposite direction due to different orientations of thevanes 121. The relative angular velocity of the turbines 120, 140 isequal to the difference between their respective angular velocities,defining rotation of the first turbine 120 as positive and the secondturbine 140 a negative. In other words, the relative angular velocity isequal to the sum of the magnitude of the respective angular velocities.Assuming the turbines 120, 140 both rotate at the same speed, therelative angular velocity is twice the angular velocity relative to astationary reference frame.

In the illustrated embodiment, the VAWT assembly 100 includes magneticlift bearings 112 configured to magnetically suspend the lower turbine120 above the lower plate 110 and to magnetically suspend the upperturbine 140 above the middle plate 130, thereby reducing rotationalfriction. In one embodiment, the magnetic lift bearing 112 for the lowerturbine 120 is a two part bearing, with a first half that includes anannular magnet or collection of magnets imbedded or otherwise attachedto the lower plate 110. The first half of the magnetic lift bearing 112is axially aligned with the lower turbine. The second half of themagnetic lift bearing 112 is imbedded or otherwise attached to thebottom of the lower turbine 120. This second half of the magnetic liftbearing 112 is axially aligned and immediately adjacent to the bearing'sfirst half, and is oriented to provide an opposing magnetic field therepels the magnetic field from the magnets in the bearing's first half.Accordingly, the two halves of the magnet lift bearing 112 providerepelling forces between the lower plate 110 and the lower turbine 120sufficient to overcome the weight of the lower turbine and to suspendthe lower turbine above the lower plate. A similar magnetic lift bearing112 is provided on the middle plate 130 and the bottom of the upperturbine 140 to magnetically suspend the upper turbine above the middleplate. In some embodiments, the magnetic lift bearings 112 can be madeof permanent rare-earth magnetic material. In other embodiments, thelift bearings 112 are made of electromagnets that can be switched on oroff.

In at least one embodiment, the VAWT assembly 100 includes magneticcompression bearings 113 that provide compressive forces against thelower and upper turbines 120 and 140. The compression bearings 113 aretuned to help stabilize rotation of the lower and upper turbines 120 and140, particularly at higher operating speeds. In illustrated embodimentone magnetic compression bearing 113 is provide between the middle plate130 and the top of the lower turbine 120. Another magnetic compressionbearing 113 is provided between the top plate 150 and the top of theupper turbine 140. The magnetic compression bearings 113 can be similarto the magnetic lift bearings discussed above. For example, an uppermagnetic compression bearing 113 can include a first annular magnet ringin the top plate 150 and a second, opposing magnetic ring in the top ofthe upper turbine 140 immediately adjacent to and in axial alignmentwith the first annular magnet ring. The lower magnetic compressionbearing 113 can include a first magnet ring in the middle plate 130 andan opposing magnetic ring in the top of the lower turbine 120immediately adjacent to and in axial alignment with the first annularmagnet ring.

The compression bearings 113 are configured to provide a slightcompressive or downward force on the lower and upper turbines 120 and140 that slightly counteract the levitation forces of the magnetic liftbearings 112, thereby helping to stabilize rotation of the turbines 120,140. This compressive or downward force is less than the lifting forceprovided by the magnetic lift bearings 112, such that the magneticcompression bearings 113 do not overpower the magnetic lift bearings112. In one embodiment, the lower magnetic compression bearing 113 caninclude the magnetic rings positioned radially inward or outward of themagnetic lift bearings 112 to avoid any potentially adverse magneticinterference between the bearings. In another embodiment, the magneticcompression bearings 113 and the magnetic lift bearings 112 can bespaced at approximately the same radial dimension from the central axisof rotation of the turbines. With the lift bearings 112 and compressionbearings 113 in place, the turbines 120, 140 rotate about the shaft 160without contacting any of the plates 110, 130, or 150, and in a steady,efficient path without substantial vertical oscillation during rotation.

In some embodiments, the assembly 100 includes a rotation-assist device239, such as a motor 240 (FIG. 2), coupled to the turbines 120, 140 andconfigured to provide rotational assistance to the turbines 120, 140when needed. The motor 240 can be used to help initiate or sustainrotation of the turbines 120, 140, particularly at low wind speeds. Thewind speed necessary to initiate rotation of the wind turbines 120, 140from a stopped position is called the “break-in speed.” The break-inspeed is generally higher than the minimum steady state speed at whichthe wind turbines 120, 140 will continue to rotate. The concept issimilar to static friction being greater than dynamic friction. Whenambient wind is at or above the steady state speed, but below thebreak-in speed and the wind turbines 120, 140 will remain stopped,thereby losing an opportunity to convert the energy to useful power. Themotor 240 is configured to provide assistance to begin rotation of thewind turbines 120, 140 up to the steady-state speed when ambient windwill continue the rotation of the wind turbines 120, 140. The motor 240can also be configured to help maintain rotation of the wind turbines120, 140, particularly when the wind speed is fluctuating above andbelow the break-in speed or the steady state speed to maintain rotation.While the above-described embodiment uses a motor 240 as therotation-assist device, other embodiments can use other rotation assistdevices 239, such as an electro-magnetic-assist device configured toprovide a rotational force to one or both wind turbines, particularlywhen the wind speed is below the break-in speed.

The rotation-assist device 239, such as the motor 240, can be powered bysolar panels 230 placed on top of the upper plate 150, on or adjacent tothe supports, or in another location, including a location spaced apartfrom the assembly. The rotation-assist device 239 can also be powered byenergy from an electrical grid to which the assembly 100 is coupled, orby energy generated by the wind turbines 120, 140 and stored in abattery or other power storage device. In some embodiments, therotation-assist device 239 draws power from one or more of these sourcesto rotate only the first wind turbine 120 or only the second windturbine 140 until the assembly 100 reaches a state where sufficientenergy is being produced to rotate other wind turbines in the assembly100.

The vanes 121 of the turbines 120, 140 have an airfoil configuration,with a front side having a longer airflow surface than a back side. Thiscreates a pressure differential that rotates the wind turbines 120, 140.The turbines 120, 140 are rotated by wind passing in any directionacross the turbines 120, 140. This directional independence allows theturbine assembly 100 to be used where wind is present but is notnecessarily oriented in a predictable direction. More details on theshape, size, operation, and configuration of vanes for a wind turbineare given in U.S. Pat. No. 5,083,039 and U.S. Pat. No. 7,452,185, bothof which are incorporated herein by reference in their entirety.

In some embodiments, the bottom plate 110 and top plate 150 of theassembly 100 cooperate with the lower and upper turbines 120, 140,respectively, to provide single-rotation alternators 145 for generatingelectricity. The rotation of the turbines 120 and 140 relative to thebottom and top plates 110 and 150, respectively, is used to generateelectricity from the rotation of the turbines 120, 140 caused by thewind passing through the turbines 120, 140. Each single-rotationalternator 145 includes a stator 124 and a rotor 142. Thesingle-rotation alternator 145 for the lower turbine can include thestator 124 or the rotor 142 on the bottom plate 110, and the other oneof the rotor 142 or stator 124 is coupled to the bottom of the lowerturbine 120. Similarly, a single-rotation alternator 145 for the upperturbine can include the stator 124 or rotor 142 on the top plate 110,and the other of the rotor 142 or stator 124 on the top of the upperturbine 140. In at least one embodiment, the single-rotation alternators145 can include electro-magnetic devices so that the alternators can beselectively turned on and off. In other embodiments, the single-rotationalternators 145 can include fixed magnets, such as rare-earth magnets.

The assembly 100 of the illustrated embodiment includes acounter-rotation alternator 155 coupled to the lower and upper turbines120, 140 to produce electricity from the relative rotation between thelower turbine 120 and the upper turbine 140, as discussed above. In oneembodiment, the lower turbine 120 includes a stator 124 and the upperturbine 140 comprises a rotor 142. The stator 124 is an interior surfaceof the turbine 120 that receives the rotor 142 which appends from theupper turbine 140 and extends down through an annulus 131 of the middleplate 130. In another embodiment, the upper turbine 140 includes thestator 124 and the lower turbine 120 comprises a rotor 142. The assembly100 having the counter-rotation alternator 155 can be included inembodiments that also have one or more of the single-rotationalternators 145 discussed above. In other embodiments, the assembly 100can include just one or more of the single-rotation alternators 145 orjust the counter-rotation alternator 155. In at least one embodiment,the counter-rotation alternator 155 can include electro-magnetic devicesso that the alternator can be selectively turned on and off. In otherembodiments the counter-rotation alternator 155 can utilize fixedmagnets, such as rare-earth magnets. The terms “rotor” and “stator” areused herein to refer to the respective roles of the equipment in thealternator configuration. The term “stator” in some alternatorterminology can mean that the stator is stationary and does not rotate.In the embodiments shown in FIGS. 1 and 2, the stator 124 rotatesrelative to a stationary reference frame and relative to the rotor 142.

In some embodiments, the wind turbine assembly 100 is scalable and caninclude three, four, or more vertically stacked wind turbines, eachseparated by a plate and aligned on one or more coaxial central shafts.For purposes of illustration, however, the assembly 100 is describedhaving two wind turbines 120, 140. The plates 110, 130, and 150 can haveseveral tabs 111 extending outwardly from a circumference of the plates110, 130, and 150. The tabs 111 can be attached to a supporting bracket119 (FIG. 1) that can hold the plates 110, 130, and 150 in placerelative to the wind turbines 120, 140. The supporting brackets workwith the plates 110, 130, 150 to provide a sturdy frame or sub-structurethat securely and fixedly holds the assembly in a stable arrangement.The sub-structure can be mounted in a desirable location to expose theassembly's wind turbines to the wind. For example, the sub-structure ofthe assembly 100 can be mounted on top of a tall pole or other supportstructure to position the assembly in an elevated location relative tothe ground, a building, or other support surface.

These turbines 120, 140 of the assemblies 100 provide substantialbenefits over conventional Horizontal-Axis Wind Turbines (HAWT). Forexample, the wind turbines 120, 140 in the VAWT assemblies 100 are lesssusceptible to damage from bird strikes, because the spinning vanes 121are visible to birds, so the birds do not try to fly through theturbines. The blades of conventional HAWTs move such that birds can seethrough or past the spinning blades, thereby giving the appearance tothe birds that they can fly through the spinning blades. The VAWTassembly 100 also requires a smaller footprint and spacing relative toadjacent VAWT assemblies 100. Conventional HAWT's typically require avery large foot print and spacing between adjacent HAWTs.

FIG. 3 is a side view of a wind turbine assembly 200 in accordance withembodiments of the present disclosure. Several of the features of theassembly 200 are similar to the embodiments of the assembly 100discussed above with reference to FIG. 1. Like reference numerals areused in FIGS. 1, 2, and 3 where appropriate. In this embodiment, themiddle plate 130 includes an annulus 131, and the second wind turbine140 can include a rotor 142. The first wind turbine 120 can have astator 124 that receives the rotor 142. The rotor 142 and the stator 124can form a nested alternator that generates electricity when the firstwind turbine 120 and second wind turbine 140 counter-rotate. Asmentioned above, the terms “rotor” and “stator” refer more appropriatelyto the roles these components play in the alternator, and not to thefact that rotors conventionally rotate and stators conventionally donot. The affect of the counter-rotating wind turbines 120, 140, andtheir respective rotor 142 and stator 124 is to provide a greaterrelative angular velocity of the rotor 142 and stator 124.

FIG. 4 is an exploded view of other embodiments of a vertically-orientedcounter-rotating wind turbine assembly 300 according to the presentdisclosure. The assembly 300 includes a lower plate 110, a lower turbine120, a middle plate 130 a, an upper turbine 140, and an upper plate 150generally similar to the assemblies 100, 200 discussed above. In thisembodiment, the middle plate 130 a is a flat plate without a centralhole. The upper turbine 140 does not include the downward projectingrotor 142. Rather, the upper turbine 140 and lower turbine 120 rotaterelative to the middle plate 130 a to generate electricity. The middleplate 130 a includes levitation bearings 112 on a top side andcompression bearings 113 on a bottom side.

FIG. 5 is a side view of a wind turbine assembly 300 according toseveral embodiments of the present disclosure. The assembly 300 can besimilar to the embodiments discussed above with reference to FIGS. 1-4.Similar reference numerals are used in FIG. 5. FIG. 5 schematicallyshows a battery 210, an electrical grid 220, solar panels 230, a motor240, an anemometer 250, and a control system 260. The battery 210 can beused to store electricity produced by the assembly 300. Any appropriatebattery type can be used, and can be scaled to accommodate the size ofthe assembly 300. The electrical grid 220 can be a municipal electricalgrid. The assembly 300 can be configured to deliver electricity to thegrid, and in some cases described herein, to draw electricity from thegrid 220. The solar panels 230 can be used in connection with the windturbine to generate electricity as conventional solar panels, and alsoto power the motor 240 in a manner described more fully below. The solarpanels 230 can be placed on the upper plate 150 and can be at leastgenerally coextensive with the plate to maximize available exposedspace. Alternatively, the solar panels 230 can be located elsewhere.

The control system 260 of the illustrated is coupled to the anemometer250, and the control system uses wind speed information from theanemometer 250 to determine when and how much electricity needs to bedrawn from the solar system and/or the battery (or other electricitystorage device) to initiate rotation of one or both of the turbines 120,140. In one embodiment, one or more of the alternators 145 and 155 is anelectromagnetic device that can be turned on and off, and the controlsystem 260 is configured to selectively turn one or more of thealternators on and off based upon the rotational speed of the windturbines 120, 140 and/or the wind speed (determined by the anemometer250). For example, the control system 260 can turn off the alternators145 and/or 155 when the wind speed drops below the break-in speed orwhen rotational speed of the wind turbines 120, 140 is approaching theminimum steady-state speed. When the alternators 145, 155 are turnedoff, they do not create additional resistance to rotation of theturbines 120, 140. When the wind speed and/or rotational speed isgreater than a selected speed (i.e., the break-in speed), such that therotation of the wind turbines 120, 140 can overcome additionalresistance to rotation, the control system 260 can turn on one or moreof the alternators 145, 155, so as to begin generating electricity fromthe alternators.

In one embodiment, the control system 260 is configured to sequentiallystagger the activation of the alternators 145, 155 based upon wind speedand rotational speed of the turbines 120, 140. For example, thealternators 145, 155 are off when the wind turbines 120, 140 arestopped. When the wind speed is at or above the break-in speed and theturbines 120, 140 are rotating (either with or without assistance fromthe motor 240 or the other rotation-assist device), the control system260 turns on or otherwise activates at least one of the single-rotationalternators 145. When the wind speed is at or above the steady-statespeed, the other single-rotation alternator 145 and/or thecounter-rotation alternator 155 are turned on to maximize powergeneration from the spinning turbines 120, 140. The control system 126can also be configured to activate the compression bearings 113,discussed above, before or after activation of the alternators 145, 155to maintain smooth and efficient turbine rotation.

FIG. 6 is a flow chart of a method 400 of initiating rotation of thewind turbine assemblies 100, 200, and 300 shown above according to thepresent disclosure. As discussed above, the break-in speed for windturbine assemblies is generally higher than a steady state speed. Themethod 400 can be executed by a controller 260 as shown in FIG. 6, suchas a programmable logic controller. In step 405, the controller 260(FIG. 4) determines whether the anemometer 250 (FIG. 4) is active so asto determine the wind speed. If the anemometer 250 is active, thecontroller 260 determines in step 410 whether the turbines 120, 140 arestill or moving. The method 400 can include a periodic check of windturbine speed and/or wind speed, or a sensor can measure turbine speedto determine when the turbines 120, 140 stop rotating. At step 420 thecontroller determines whether the ambient wind is strong enough tosustain rotation of the wind turbines 120, 140 if they were rotating. Insome embodiments, this check can be performed by the anemometer 250(FIG. 4) and reported to the controller 260. If the wind is not strongenough, the method 400 can include a periodic check of wind speed. Whenthe wind speed is measured approximately at or above a sustainable levelabove the steady state speed, at which point the method 400 can includestarting a motor 240 at step 430 to rotate one or more of the windturbines 120, 140. The motor 240 can be activated to help initiaterotation of wind turbines 120, 140 independently or simultaneously. Atstep 440, the method 400 can include a check of whether the wind isstill blowing above the steady state speed. If so, the motor 240 cancease at step 450. If the wind has dropped below the steady state speed,however, the method 400 can return to step 410 and the process repeats.Step 440, checking for a sustainable condition, can include a waitperiod to ensure an accurate check and to prevent a momentary wind dropfrom stopping the method 400. The time of the wait period can depend onthe environment in which the wind turbine operates. If ambient wind isreasonably predictable and stable, the wait period can be shorter thanfor wind turbines in other places where wind is less reliable.

If the controller determines, at step 410, that the turbines are moving,the controller can determine at step 455 whether the wind speed, asmeasured by the anemometer, is at or above a high-rate wind threshold.If the wind speed is at or above the high wind threshold, which canindicate substantially sustained rotation of the turbines at asufficient speed, the controller can be configured, at step 460, topower or otherwise activate the compression bearings 113, discussedabove. As discussed above, the wind turbine assemblies 100, 200, and 300can include magnetic lift bearings 112 and magnetic compression bearings113. In some applications, the bearings can have an effect on requiredthe break-in speed. To overcome this, the compression bearings 113 caninclude electromagnets that can be switched on and off. The compressionbearings 113 can be switched off when the turbines 120, 140 are stoppedso as to lower the break-in speed. The compression bearings can also beswitched off or remain off when the rotational speed of the turbines isclose to the minimum steady state speed. The method 400 can power thecompression bearings 113 thereby activating the compressive forces onone or both wind turbines 120, 140 when wind turbines are rotating at orabove a selected speed relative to the minimum steady state speed. Inanother embodiment, the compression bearings 113 can be turned on andoff based upon the measured wind speed. For example, if the measuredwind speed drops below a threshold level, the compression bearings 113can be turned off to allow the wind turbines to continue spinning withless resistance while the wind speed is low, thereby taking advantage ofthe inertia of the spinning turbines in low wind speed conditions.

The method 400 can also include a step 470 of powering or otherwiseactivating one or more of the alternators 145 and/or 155 when thecontroller determines at step 455 that the wind speed is at or above thehigh wind threshold. The controller can be configured to activate thecounter-rotating alternator 155 without activating the single-rotatingalternators 145. The controller 260 can also be configured to turn on orotherwise activate the single-rotation alternators 145 sequentially(e.g., as a function of the wind speed), or simultaneously. Thecontroller 260 can also be configures to activate all of the alternators145, 155 substantially simultaneously, such as when the wind speed ishigh enough, thereby spinning both turbines and generating the maximumenergy from the assembly via the single-rotation alternators 145 and thecounter-rotation alternator 155. The controller 260 can also beconfigured to selectively turn off the alternators when the wind speedand/or the turbines' rotational speed drop below one or more thresholdvalues, thereby maximizing the efficiency of the energy generation bythe assembly.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Additionally, aspects of theinvention described in the context of particular embodiments or examplesmay be combined or eliminated in other embodiments. Although advantagesassociated with certain embodiments of the invention have been describedin the context of those embodiments, other embodiments may also exhibitsuch advantages. Additionally not all embodiments need necessarilyexhibit such advantages to fall within the scope of the invention.

1. A wind turbine assembly, comprising: a shaft oriented at leastgenerally vertically; a lower plate oriented at least generallyhorizontally with the shaft passing through a portion of the lowerplate; a first wind turbine adjacent to the lower plate, the first windturbine comprising a plurality of vertically-oriented air foil vanesarranged at a periphery of the first wind turbine, wherein the vanes areshaped such that wind passing over the vanes causes the first windturbine to rotate in a first direction relative to the shaft; a middleplate adjacent to the first wind turbine and oriented at least generallyhorizontally with the shaft passing through a portion of the middleplate; a second wind turbine adjacent to the middle plate, the secondwind turbine being substantially similar to the first wind turbine,wherein the second wind turbine has a plurality of air-foil vanes shapedsuch that wind passing over the vanes causes the second wind turbine torotate in a second direction relative to the shaft; a rotor on the firstwind turbine; a stator on the second wind turbine, wherein the rotor andstator are configured to rotate relative to one another to generateelectricity; and an upper plate adjacent to the second wind turbine andoriented at least generally horizontally with the shaft passing througha portion of the upper plate.
 2. The wind turbine assembly of claim 1wherein the middle plate comprises a first middle plate, and wherein theassembly further comprises a third wind turbine and a second middleplate between the second wind turbine and the third wind turbine.
 3. Thewind turbine assembly of claim 1 wherein the upper plate comprises asolar panel.
 4. The wind turbine assembly of claim 1 wherein: the medianplate comprises an annulus, the rotor extends downward from the upperturbine through the annulus, and the stator comprises a recession in thefirst wind turbine configured to receive the rotor.
 5. A method ofinitiating rotation of a wind turbine, comprising: detecting an ambientwind speed around the wind turbine; comparing the wind speed to apredetermined steady-state wind speed and to a break-in wind speed; andif the wind turbines are not rotating, and if the wind speed is at orabove the steady-state wind speed but below the break-in wind speed,rotating the wind turbines with a motor until the wind turbines reach asteady-state operating speed.